In the art of dispensing tool assemblies of the general type disclosed in Pat. No. Reissue 34,426 and U.S. Pat. No. 4,889,149 issued to the assignee of the present invention, it is sometimes desirable to construct a tool assembly for evacuating and charging a liquid receiving system such as a liquid coolant system for an internal combustion engine. One form of liquid charging tool assembly is disclosed in connection with FIGS. 11-14 of above-mentioned U.S. Pat. No. 4,889,149. This tool assembly is adapted to be connected to an inlet fitting for a radiator of an engine coolant system in place of the radiator cap for first evacuating air and moisture from the system and then charging the system with a predetermined volume of liquid coolant. As shown in FIG. 13 of the '149 patent, the tool assembly incorporates a set of annular pistons for clamping on and sealing with the radiator inlet fitting and also for operating a valve within the center outlet passage. Another form of a fluid or refrigerant charging tool assembly is disclosed in U.S. Pat. No. 4,869,300. This tool assembly incorporates a pair of cam actuated arcuate ring sections for securing or clamping the tool assembly to a Schrader type valve stem.